drm/i915/edp: Do not do link training fallback or prune modes on EDP

drm/i915/edp: Do not do link training fallback or prune modes on EDP

In case of eDP because the panel has a fixed mode, the link rate
and lane count at which it is trained corresponds to the link BW
required to support the native resolution of the panel. In case of
panles with lower resolutions where fewer lanes are hooked up internally,
that number is reflected in the MAX_LANE_COUNT DPCD register of the panel.
So it is pointless to fallback to lower link rate/lane count in case
of link training failure on eDP connector since the lower link BW
will not support the native resolution of the panel and we cannot
prune the preferred mode on the eDP connector.

In case of Link training failure on the eDP panel, something is wrong
in the HW internally and hence driver errors out with a loud
and clear DRM_ERROR message.

v2:
* Fix the DEBUG_ERROR and add {} in else (Ville Syrjala)

Cc: Clinton Taylor <[email protected]>
Cc: Jim Bride <[email protected]>
Cc: Jani Nikula <[email protected]>
Cc: Ville Syrjala <[email protected]>
Cc: Dave Airlie <[email protected]>
Cc: Daniel Vetter <[email protected]>
Signed-off-by: Manasi Navare <[email protected]>
Reviewed-by: Ville Syrjala <[email protected]>
Reference: https://bugs.freedesktop.org/show_bug.cgi?id=103369
Signed-off-by: Imre Deak <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]